This invention relates generally to an electrophotographic printing machine, and more particularly concerns an improved apparatus for supporting and controlling the lateral movement of a moving photoconductive belt.
In the process of electrophotographic printing, a photoconductive belt is charged to a substantially uniform potential so as to sensitize the surface thereof. Thereafter, the sensitized surface of the photoconductive belt is exposed to a light image of an original document being reproduced. Exposure of the charged portion of the photoconductive belt selectively discharges the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive belt corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive belt, the latent image is developed by bringing a developer mix into contact therewith. Generally, the developer mix comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image so as to form a toner powder image on the photoconductive belt. The toner powder image is then subsequently transferred to a copy sheet. Finally, the copy sheet is heated to permanently affix the toner particles thereto in image configuration. This general approach was originally disclosed by Carlson in U.S. Pat. No. 2,297,691 and has been further amplified and described by many related patents in the art.
The location of the latent image recorded on the photoconductive belt must be precisely defined in order to have the various operating stations act thereon to optimize copy quality. To this end, it is critical that the lateral alignment of the photoconductive belt be controlled within prescribed tolerances. Only in this manner will the photoconductive belt move through a pre-determined path so that the processing stations disposed thereabout will be located precisely relative to the latent image recorded thereon.
When considering control of the lateral movement of the photoconductive belt, it is well known that if the belt were constructed and entrained about perfectly cylindrical rollers mounted and secured in an exactly parallel relationship with one another, there would not be any lateral movement of the belt. In actual practice, however, this is not feasible and the location of the photoconductive belt must be controlled to regulate its lateral position.
Accordingly, it is a primary object of the present invention to improve the apparatus for supporting and controlling the lateral movement of the photoconductive belt employed in an electrophotographic printing machine.